Boy+ is when one identify completely as a boy, plus additional genders. One doesn't feel partially boy, one isn’t fluid - one is entirely a boy, plus more. One may not know specifically what the additional gender/genders are, so boy+ may be the best way to describe it. Or, one may have a lot of genders, but they all feel like they are simply additional while one's main gender is boy/man/guy/male, etc.
History and Flag
This term was coined by Tumblr user moonviewcrew on 27th May, 2021. The flag was created on the same day.[1]